Electronic timing systems are commonly used for pool swimming races, with the recording of swimmers' start times, lap times (often referred to as split times), and finish times commonly being triggered by switches known as “touchpads”. The touchpads are typically large, flat panels mounted underwater against the wall of the pool at the end of each swimming lane, positioned for a swimmer to make switch-closing contact with his hands or feet at the end of each lap. The touchpads are connected to a timing system that associates a start time, split time, or final time with each contact.
Switch sensitivity, speed, and dependability are critical given the precision expected of timing systems in modern swimming competition. Prior touchpads, however, often suffer from drawbacks in one or more of these categories. Typical touchpad construction is a sandwich of metal plates and internal switch contact surfaces in either an open, unsealed construction in which water flows freely over the switch contacts and other internal portions of the pad, or a sealed construction in which water is sealed out while the interior is pressurized to maintain proper switch sensitivity at varying pressures. As noted in U.S. Pat. No. 3,944,763 to Beierwaltes, unsealed touchpads are subject to corrosion, which leads to reduced switch sensitivity and even switch failure. Sealed, air-filled touchpads are sensitive to air and water pressure variations, and need frequent pressure adjustments to maintain proper spacing between the internal switch contact surfaces. While sealed touchpads are not subject to internal corrosion to the same extent as open-construction touchpads, they commonly use multiple layers of screen and foam that are not particularly sensitive or consistent and that are prone to compression set and degradation over time.
U.S. Pat. No. 6,156,987 to Warne discloses an open, unsealed, water-filled touchpad with three metal plates (thicker backplate, flexible thin faceplate, and flexible thin middle plate) spaced by non-conductive foam tape strips in staggered vertical rows, or in discontinuous horizontal rows, to define vertical drain passages for water when the touchpad is lifted from the water. The foam tape strips are said to be sufficiently resilient that a light touch on the faceplate either between or in line with the strips deflects the faceplate into the middle plate or the middle plate into the backplate, respectively. Upon release of the touch, the faceplate and middle plate return to their spaced-apart relationship. Brackets secured to the backplate around the edges of the touchpad are angled to overlie the faceplate edges to secure the vertical edge margins of the plates against movement outwardly and away from each other. To fight switch contact corrosion and plating problems in this unsealed touchpad, Warne uses heavy and expensive passivated stainless steel for the plates, and emphasizes the use of a very low DC voltage (around 0.25 volts) for the switch current through the plates. There appears to be no attempt to address the problems of foam inconsistency and degradation over time as noted by Beierwaltes, and since the foam tape strips are submerged in water they are believed to be even more prone to these problems than in sealed touchpad construction.